Crystal structure of golyshevite

The crystal structure of golyshevite, a new calcium-and carbon-rich representative of the eudialyte group, was established by single-crystal X-ray diffraction analysis (sp. gr. R 3 m , a = 14.231(3) Å, c = 29.984(8) Å, R = 0.062, 1643 reflections with F > 3σ( F )). The idealized formula of golyshevite is (Na 10 Ca 3 )Ca 6 Zr 3 Fe 2 SiNb[Si 3 O 9 ] 2 [Si 9 O 27 ] 2 (OH) 3 (CO 3 ) · H 2 O. This mineral is characterized by the presence of calcium atoms both in the octahedral positions of six-membered rings and in extraframework positions, where calcium prevails. CO 3 groups are present as the major additional anions. Carbon atoms randomly occupy two positions on the threefold z axis at a distance of 0.75 Å from each other and are coordinated by oxygen atoms arranged around the z axis.